6. Project Abstract: Identifying unnecessary irradiation of patients with suspected renal colic Up to 12% of the population has kidney stones, and 3-5% of all persons are likely to experience an episode of renal colic in their lifetime, many of whom will present to the Emergency Department (ED) for evaluation. Computed tomography (CT) scanning is now a first-line test for suspected renal colic, and is accurate in detecting stones. However CT scanning involves significant amounts of ionizing radiation, is costly, may lead to further unnecessary testing, and rarely alters management as most kidney stones pass spontaneously. CT scanning has increased dramatically in the U.S. over the last several decades, from approximately 3 million scans done in 1980 to over 60 million in 2007. In the year 2000 there were ~12 scans per 100 people, nearly doubling to ~22 per 100 people in 2005; during that time Medicare expenditures for imaging increased from $6.2 billion to $12 billion, accounting for 23% of all Medicare spending in 2005. Long term, the radiation received from a single CT scan of the abdomen/ pelvis has been estimated to cause approximately 12 deaths for every 10,000 scans performed. While other rules for imaging have been developed and implemented in the emergency setting, there is no decision rule to guide the use of appropriate imaging in suspected renal colic. We propose to derive, validate, and test the implementation of a decision rule that will allow appropriate use of CT scan in patients evaluated for suspected renal colic. The derivation set will consist of retrospectively derived data from all patients at our institution over a 4-year period who underwent a CT flank pain protocol (CT FPP) for suspected kidney stone. Classification and regression tree (CART) analysis will be utilized to derive a rule that will reliably predict the presence of kidney stone, as well as stones requiring intervention (6mm or greater), and other urgent or emergent diagnoses likely to require intervention. Once derived, this rule will be prospectively validated using point-of-care clinician performed ultrasound, plain films when appropriate, and data from the electronic medical record. In the final phase the rule will be implemented by physician training and incorporation into the computerized physician order entry (CPOE) system. The performance of the rule will be measured against CT findings and intervention during a 90-day follow-up period. Impact of the rule and cost benefit analysis will be evaluated to determine the comparative effectiveness of the derived rule. We anticipate a rule can be derived and validated, improving patient safety and reducing cost by reducing imaging that will not alter management in suspected renal colic.